JPH07316309A - Continuous medium recirculation pulverization method - Google Patents

Abstract

PURPOSE: To obtain submicron particles of a compound useful in image formation in good operability by continuously introducing the compound and a rigid milling medium into a milling chamber to reduce the particle size of the compound and separating the compound from the medium in a different place.

CONSTITUTION: A compound 10 useful for imaging elements and a rigid milling medium 12 are continuously introduced into a milling chamber 14 having a rotary shaft 16, and the dispersion containing the compound 10 and the medium 12 are recirculated into a holding tank 20 by a peristaltic pump 18. The milling medium is separated from the compound useful for image formation by a second process such as simple filtration or a mesh screen without providing the milling chamber with a milling medium retention means such as a screen or a rotary gas separator. The milling medium comprises e.g. beads of a polymer resin and has a mean particle size of 5-1,000 μm, desirably, 300 μm.

COPYRIGHT: (C)1995,JPO

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION This invention relates to a continuous recycle milling process for obtaining small particles of materials such as pigments used in paints and compounds useful in imaging elements.

[0002]

BACKGROUND OF THE INVENTION Traditional mills used to reduce size in a continuous fashion typically incorporate means for holding the milling media in the milling zone (eg, milling chamber) of the mill, which may be used as a dispersion or The slurry can be passed from the mill to a stirred holding vessel during recirculation. Various techniques for holding media in these mills have been established, such as rotating gap separators, screens, screens, centrifugal auxiliary screens, and similar devices that physically limit the passage of media from the mill. The last decade has shifted to the use of smaller grinding media in the traditional media grinding methods of preparing various paints, pigment dispersions and photographic dispersions. This transition is mainly due to mills that use media as small as 250 μm (eg Netzsch LM
This is made possible by improvements in the mill design of C mills and Drais DCP mills. Advantages of small media include more efficient milling (i.e., faster speed milling) and smaller ultimate particle size. 250 μ even with the best machine designs available due to unacceptable pressure build-up due to separation screen blockage and media hydraulic blockage
It is generally not possible to use media smaller than m. In fact, for many commercial applications, 350 μm media is considered a practical lower limit for many systems due to the limitations of media separation screens.

[0003]

We have identified various problems associated with the prior art processes required to separate dispersed particles from the grinding media in a grinding chamber (eg, separation screen clogging, and media hydraulics). We have discovered a continuous milling method that prepares very fine particles that avoids unacceptable pressure buildup due to static clogging.

[0004]

We address the aforementioned media separation problems during milling by 1) adjusting the media separator to allow the media to pass through the separator. 2)
It has been found that this can be avoided by providing a means of continuously recycling the medium / product mixture throughout the process.

One aspect of the present invention comprises a continuous process for preparing submicron particles of a compound useful in an imaging element, the process comprising the steps of: a) the compound and hard grinding media in a grinding chamber. B) contacting the compound with the grinding medium to reduce the particle size of the compound in the grinding chamber, c) continuously introducing the compound and the grinding medium from the grinding chamber. And then d) separating the compound from the grinding media.

Another aspect of the present invention comprises a continuous process for preparing submicron particles of a compound useful in an imaging element, the process comprising the steps of: a) said compound in a grinding chamber, hard ground. Continuously introducing a medium and a liquid dispersion medium, b) wet milling the compound with the milling medium to reduce the particle size of the compound in the milling chamber, c) the compound from the milling chamber, Continuously removing the grinding medium and the liquid dispersion medium, and then d) separating the compound from the grinding medium.

Through the process of the present invention, particles of a compound useful in an imaging element and hard grinding media are continuously introduced into a mill in which grinding is carried out continuously to reduce the average particle size of said compound.

[0008]

DETAILED DESCRIPTION OF THE INVENTION The present invention is directed to milling materials such as paint pigments and compounds useful in imaging elements to obtain very fine particles. The term "continuous method" is
The compound to be dispersed and the grinding medium are introduced continuously,
And it means that it is continuously removed from the grinding chamber.
This can be in contrast to the conventional roller mill process in which the compound to be ground and the grinding media are introduced in a batch process and removed from the grinding chamber.

The term "compounds useful in imaging elements" refers to compounds which can be useful in photographic elements, electrophotographic elements, thermal transfer elements and the like. Although the present invention is described primarily with respect to the use of compounds useful in imaging, it will be understood that the present invention is applicable to a wide variety of materials.
In the present invention, as compared to the medium normally present in the milling chamber of the process, this medium is incorporated as an additive into the dispersion to be milled in constant concentration. The media concentration can vary from 10 to 95% by volume depending on the application and will be selected based on the milling requirements and the fluid properties of the mixed media and dispersion.

The size of the medium in question is 5 μm to 1000
The media separator gap can be adjusted according to a size of about 2 to 10 times the maximum media particle size present. The composition of the medium can include glass, ceramic, plastic, steel, and the like. In a preferred embodiment, the milling material may consist of particles (preferably substantially spherical in shape, eg beads), especially particles composed of polymeric resins.

Generally, polymeric resins suitable for use in the present invention are chemically and physically inert, are substantially free of metals, solvents and monomers, and are chipped or crushed during milling. It has sufficient hardness and friability so that it can be prevented. Suitable polymer resins include cross-linked polystyrene (such as polystyrene cross-linked with divinylbenzene), styrene copolymers, polyacrylates (such as polymethylmethacrylate), polycarbonates, polyacetals (Derli).
n: trademarks, etc.), vinyl chloride polymers and copolymers, polyurethanes, polyamides, poly (tetrafluoroethylene) s (eg, Tefron: trademark) and other fluoropolymers, high density polyethylenes, polypropylenes, Cellulose ethers and esters (cellulose acetate and the like), polyhydroxymethacrylate, polyhydroxyethyl acrylate, silicone-containing polymers (polysiloxanes) and the like are included. The polymer can be biodegradable. Typical biodegradable polymers include poly (lactide), poly (glycolide), lactide and glycolide copolymers, polyanhydrides, poly (hydroxyethylmethacrylate), poly (iminocarbonate), poly (N-acylhydroxyproline). ) Esters, poly (N-palmitoyl hydroxyprilino) esters, ethylene-vinyl acetate copolymers, poly (orthoesters), poly (caprolactone), and poly (phosphazenes).

This polymer resin contains 0.9 to 3.0 g /
It can have a density of cm ³ . Higher density resins are preferred. This is because they are believed to reduce particle size more efficiently. The preferred method of making the polymer grinding media is by suspension polymerization of acrylic and styrene monomers. Methyl methacrylate and styrene are the preferred monomers because they are inexpensive, commercially available materials that make acceptable polymer grinding media. Other acrylic and styrene monomers are described as effective. Styrene is preferred. However, free radical addition polymerization in general, and suspension polymerization in particular, are not 100% completely viable. The residual monomer that leaches out during the milling process remains in the beads, contaminating the resulting dispersion.

Removal of residual monomers can be accomplished by many methods common in polymer synthesis, such as heat drying, stripping with an inert gas (such as air or nitrogen), solvent extraction and the like. Drying and stripping processes are limited by the low vapor pressure of residual monomer, large bead size that results in long diffusion paths. Therefore, solvent extraction is preferred. Any solvent such as acetone, toluene, alcohol (such as methanol), alkane (such as hexane), and supercritical carbon dioxide can be used. Acetone is preferred. However, effective solvents to remove residual monomers generally dissolve the polymers made from the monomers or form tacky and difficult to handle polymers. Therefore, it is preferred to crosslink the polymer to make it insoluble in the solvent the monomer prefers.

Sufficient cross-linking agent (generally a few percent) is required to render the polymer insoluble, but any amount can be used as long as the beads serve adequately as a grinding medium. It has been found that 100% of the commercially available divinylbenzene (55% calibrated divinylbenzene) produces beads that grind and contaminate the product. Any monomer having multiple ethylenically unsaturated groups such as divinylbenzene and ethylene glycol dimethacrylate can be used. Divinylbenzene is preferred and a copolymer of 20% styrene and 80% commercial divinylbenzene (55% assay) is especially preferred.

Further, the present invention can be practiced with a variety of inorganic grinding media prepared to the appropriate particle size. Such media include zirconium oxide (such as magnesia-stabilized 95% ZrO), zirconium silicate, glass, stainless steel, titania, alumina,
And yttrium-stabilized 95% ZrO.

The medium can range in size up to 1000 μm. When milled, the particles are preferably less than about 300 μm, more preferably less than about 100 μm, even more preferably less than about 75 μm in size, and most preferably about 50 μm or less. About 25μ
Excellent particle size reduction has been achieved with media having a particle size of m, and media milling with media having a particle size of 5 μm or less is also contemplated.

The grinding process is a dry process (eg,
It can be a dry roller mill process) or a wet process (ie wet mill). In a preferred embodiment, the present invention is practiced according to the wet mill process described in US Pat. No. 5,145,684 and European Patent Application No. 498,492. Therefore, this wet milling process can be carried out with liquid dispersion media and the interfacial modifiers described in their patent specifications. Useful liquid dispersion media include water, aqueous salt solutions, ethanol, butanol, hexane, glycol and the like. The surface modifier can be selected from known organic and inorganic materials such as those described in the aforementioned patent specifications. The surface modifier can be present in an amount of 0.1 to 90% by weight, preferably 1 to 80% by weight, based on the total weight of dry particles.

In a preferred embodiment, compounds useful in imaging elements can be prepared in submicron or nanoparticulate particle sizes (eg, less than about 500 nm). The inventor has demonstrated that particles having an average particle size of less than 100 nm were prepared according to the present invention.
The ability to prepare such microparticles without unacceptable contamination was very surprising and unexpected.

Grinding can also be carried out in any suitable grinding mill. Suitable mills include air jet mills, roller mills, ball mills, grinding mills, vibration mills,
Includes planetary mills, sand mills and bead mills. If the grinding media consists essentially of the polymeric resin, a high energy media mill is preferred. The mill can have a rotating shaft. The present invention provides a Cowles disperser,
It can also be carried out with a rotor-stator mixer, or other conventional mixer that can provide high fluid velocities and high shear.

Preferred ratios of milling media, compounds useful in imaging, selective liquid dispersion media and interface modifiers are:
It can vary within wide limits and depends, for example, on the particulate material selected, the size and density of the grinding media, the type of mill selected, etc. The grinding medium concentration is about 10 depending on the application.
It can range from 95% by volume, preferably 20-90% by volume, and can be optimized based on the milling work requirements and the mixed flow properties of the milling medium and the compound to be milled.
Attrition times can vary over a wide range and depend primarily on the compounds useful for imaging, mechanical means and residence conditions selected, initial and desired final particle size, and the like. Residence times of less than about 8 hours are generally required using high energy dispersers and / or media mills.

The process can be carried out over a wide range of temperatures and pressures. Preferably this process
It is carried out at a temperature t at which the compound useful for imaging causes disassembly. Generally, temperatures of about 30 ° C to less than 40 ° C are preferred. The temperature control may be, for example, coating or immersing the grinding chamber in ice water. This process can be carried out with a wide variety of materials, especially pigments useful in paints and compounds especially useful in imaging elements. In the case of a dry mill, the compounds useful in imaging are often allowed to form solid particles. In the case of a wet mill, the compounds useful in imaging should have poor solubility and dispersibility in at least one liquid medium. "Not very soluble" means that the compound useful in the imaging element is about 1 in the liquid dispersion medium (eg, water).
It is meant to have a solubility of less than 0 mg / ml, preferably less than about 1 mg / ml. The preferred liquid dispersion medium is water. Furthermore, the invention can be practiced with other liquid media.

In a preferred embodiment of the invention, the compounds useful in the imaging element are dispersed in water and the resulting dispersion is used to prepare the imaging element. Preferably, the liquid dispersion medium contains water and a surfactant. Compounds useful in the imaging element and grinding media are continuously removed from the grinding chamber. The milling media is then separated from the milled particulate image-useful compounds using conventional separation techniques in a second process such as simple filtration, sieving with a mesh filter screen, and the like. Other techniques such as centrifugation can also be used.

Compounds useful in suitable imaging elements include
For example, a dye-forming coupler, a development inhibitor releasing coupler (DIR), a development inhibitor adjacent group (DI (A) R), a masking coupler, a filter dye, a thermal transfer dye, an optical brightener, Nucleating agent, development accelerator, oxidized developing agent scavenger, UV absorbing compound,
Sensitizing dyes, development inhibitors, antifoggants, bleaching accelerators, magnetic particles, lubricants, matting agents and the like are included.

Such compounds are described in Research Disclosure, Item 308119 198.
December 9th, (Kenneth Mason Publication Ltd., Dudley A
nnex, 12a North Street, Emsworth, Hampshire PO10 7
Published by DQ, England), Sections VII and VI
II, as well as Research Disclosure, Item 3439019
It can be found in November 1992.

In a preferred embodiment of the invention, the compounds useful in the imaging element are sensitizing dyes, thermal transfer dyes or the filter dyes described below. In general, filter dyes that can be used in accordance with the present invention are described in EP 54
No. 9,089 (Texter, etc.) and 430, 18
No. 0 and US Pat. No. 4,803,150,
4,855,221, 4,857,446, 4,900,652, 4,900,653, 4,940,654, 4,948,717, 4 , 948,718, 4,950,586, 4,988,611, 4,994,356, 5,098,820, 5,213,956, 5,260. , 179 and 5,266,454.

Generally, thermal transfer dyes that can be used in accordance with the present invention include anthraquinone dyes (eg, Smikaron Violet RS: trademark, Sumitomo Chemical C.
o., Ltd., Dianix Fast Violet 3R-FS: Trademark, Mitsu
Made by bishi Chemical Industries, Ltd. and Kayalon P
olyol Brilliant Blue N-BGM: Trademark and KST Black 1
46: Trademark, manufactured by Nippon Kayaku Co., Ltd .; Azo dye (K
ayalon Polyol BrilliantBlue BM: Trademark, Kayalon Poly
ol Dark Blue 2BM: Trademark, and KST Black KR: Trademark,
Made by Nippon Kayaku Co., Ltd, Sumikaron Diazo Black 5
G: Trademark, manufactured by Sumitomo Chemical Co., Ltd., and Mikt
azol Black 5GH: Trademark, Mitsui Toatsu Chemicals, In
c.); Direct Dark Green B: Trademark, Mitsu
Made by bishi Chemical Industries, Ltd. and Direct Br
own M: Trademark and Direct Fast Black D: Trademark, Nippo
n Kayaku Co., Ltd); Acid dye (Kayanol Milling C
yanine 5R: Trademark, manufactured by Nippon Kayaku Co., Ltd .; Basic dye (Sumiacryl Blue 6G: Trademark, Sumitomo Chemica)
Co., Ltd., and Aizen Malachite Green: trademark, manufactured by Hodogaya Chemical Co., Ltd); or US Pat. Nos. 4,541,830 and 4,698,651,
Nos. 4,695,287, 4,701,439, 4,757,046, 4,743,582, 4,769,360, and 4,753,922. Included are the dyes disclosed in the book.

Generally, sensitizing dyes that can be used in accordance with the present invention include cyanine dyes, merocyanine dyes,
Included are complexed cyanine dyes, complexed merocyanine dyes, homopolar cyanine dyes, hemicyanine dyes, styryl dyes, and hemioxonol dyes. Of these dyes, cyanine dyes, merocyanine dyes and complexed merocyanine dyes are particularly useful.

The nuclei of commonly used cyanine dyes can be applied to these dyes as the basic heterocyclic nuclei. That is, a pyrroline nucleus, an oxazoline nucleus, a thiazoline nucleus, a pyrrole nucleus, an oxazole nucleus, a thiazole nucleus, a selenazole nucleus,
Imidazole nuclei, tetrazole nuclei, pyridine nuclei, etc., and nuclei formed by condensing these nuclei with alicyclic hydrocarbon rings, and nuclei formed by condensing these nuclei with aromatic hydrocarbon rings (That is, indolenine nucleus, benzoindolenine nucleus, indole nucleus, benzoxazole nucleus, naphthoxazole nucleus, benzothiazole nucleus, naphthothiazole nucleus, benzoselenazole nucleus,
Benzimidazole nuclei, quinoline nuclei, etc.) are suitable.
Also, carbon atoms of these nuclei can be replaced.

Merocyanine dyes and complexed merocyanine dyes which can be used are pyrazolin-5-one nuclei, thiohydantoin nuclei, 2-thiooxazolidine-
2,4-dione nucleus, thiazolidine-2,4-dione nucleus,
It has a 5-membered or 6-membered heterocyclic nucleus such as a rhodanine nucleus and a thiobarbituric acid nucleus. A solid particle dispersion of a sensitizing dye is used together with a dye that does not itself enhance the spectral sensitizing effect but exhibits a supersensitizing effect, or a substance that does not substantially absorb visible light but exhibits a supersensitizing effect. Can be added to the silver halide emulsion. For example, aminostilbene compounds substituted with a nitrogen-containing heterocyclic group (for example, US Pat. No. 2,9,9).
33,390 and 3,635,721), aromatic organic acid-formaldehyde condensate (for example, described in US Pat. No. 3,743,510). ), Cadmium salts, azaindene compounds and the like.

The sensitizing dyes can be added to the silver halide grains and generally the hydrophilic colloids either before (for example during or after chemical sensitization) or at the same time the emulsion is coated on the photographic support. Immediately before or before coating with this dye / silver halide emulsion (for example, 2 hours before)
Can be mixed with a dispersion of color image-forming couplers. The above sensitizing dyes can be used alone or in combination. For example, it provides silver halide with additional sensitivity outside the wavelength of light provided by one dye, or supersensitizes the silver halide.

Particularly preferred compounds useful in imaging elements that can be used in the dispersions of this invention are the filter dyes, thermal transfer dyes, and sensitizing dyes illustrated below:

[0032]

[Chemical 1]

[0033]

[Chemical 2]

[0034]

[Chemical 3]

[0035]

[Chemical 4]

[0036]

[Chemical 5]

The above examples are only representative examples.
Please understand that not all. In a preferred embodiment,
The compound to be ground and the grinding media are recycled through the grinding chamber. Suitable examples of means for achieving recirculation include peristaltic pumps, diaphragm pumps, piston pumps, centrifugal pumps and other positive displacement pumps that do not use closely spaced tolerances to damage the grinding media.
Peristaltic pumps are generally preferred.

An alternative of the present invention involves the use of mixed media sizes. For example, larger media can be used in the conventional manner of limiting such media to the grinding chamber. The smaller grinding media can be continuously recirculated through the system and can pass through a stirred bed of larger grinding media. In this aspect,
The smaller media preferably have an average particle size of between about 1 and 300 μm and the larger grinding media comprise about 30.
Average particle size between 0 and 1000 μm.

With reference to FIG. 4, the process of the present invention can be implemented as follows. The compound (10) useful in the imaging element and the hard grinding media (12) were continuously introduced into a grinding chamber (14) having a rotating shaft (16) as shown. A peristaltic pump (18) recirculates the dispersion containing the compound and grinding media from the grinding chamber into the holding tank (20). Contrary to typical conventional processes, there is no means of holding the grinding media such as screens or rotating gap separators in the grinding chamber.

[0040]

The present invention will be specifically described with reference to the following examples. Example 1 An aqueous premixed slurry of yellow filter dye D-10 was prepared by simply mixing the following ingredients: Component Amount (g) Dye D-10 30 Triton X-200 (surfactant) 3 Polyvinylpyrrolidone ( Mw : 37,000) 4.5 Water 562.5 Total 600 This slurry was mixed with 750 g of polystyrene grinding media with an average diameter of 50 μm. Mix a mixture of filter dye slurry and media with 0.6 liters of Dyno Mill (Chicago
Boiler Company, Buffalo Grove, IL) media mill at 3000 rpm, residence time 60 minutes. This treatment involves continuously recirculating the mixture from a holding vessel which is being stirred through a media mill with a peristaltic pump at a flow rate of 100 g / min. A media separator gap of the media mill (usually adjusted to limit the media to the grinding chamber) has a clearance of 500 μm to allow the media to pass freely back from the grinding chamber to the holding vessel. Adjusted to. This configuration ensured that there was no significant accumulation of media in the grinding chamber. A media: slurry mix ratio of 1.25 was maintained throughout the process. The processing temperature was maintained at 20 ° C ± 5 ° C.

After a residence time of 60 minutes, the ground slurry was separated from the grinding media with an 8 μm filter. Samples of the unmilled premixed slurry and the milled slurry were used as high resolution capillary cartridge serial no. 208
Capillary Hydrodynamic Fractionation (Ma
tec Applied Sciences, 75 House Street, Hopinton, M
A, 01748) describes the characteristics of particle size distribution, and
Eluted with wt% diluted GR-500 aqueous eluent.

1 and 2 compare the particle size number and weight distribution of the unmilled premixed slurry and the milled slurry, respectively. The following table compares the weight average particle size of each variation: sample mean size (nm) 1-1 unmilled premix 164.9 1-2 milled slurry 123.3 As indicated, Treatment with 50 μm media in a continuous media recycle process resulted in a significant decrease in average particle size, reducing the number of particles ending in the unwanted 200 nm.

Example 2 A second premixed slurry of the same yellow filter dye was prepared as in Example 1. 600 g of this slurry is
It was mixed with 1170 g of polymethylmethacrylate grinding medium with an average diameter of 75 μm. This mixture was processed as in Example 1 and the particle size distributions of both the premixed slurry and the milled slurry were measured.

The accompanying FIG. 3 represents the particle size and weight distribution of the milled slurry relative to the unmilled slurry of FIG. The following table compares the weight average particle size of each variation: sample average size (nm) 2-1 unmilled premix 164.9 2-2 milled slurry 79.3 With these data, Different size media and example 1
It is confirmed that the average particle size can be greatly reduced by using the composition used in the treatment described in (1).

Example 3 An aqueous premixed slurry of Yellow Filter Dye D-2 was prepared by simply mixing the following ingredients: Component Amount (g) Dye D-2 40 Oleoyl Methyltaurine, Sodium Salt 8 Water 752 Total 800 Add 0.6 liters of Dyno to this filter dye slurry.
Mill Processed in a media mill at 3000 rpm with a residence time of 60 minutes. The grinding chamber of the media mill was filled with 0.48 liters of 500 μm polystyrene grinding media and the media separator gap was adjusted to 100 μm to hold the media in the grinding chamber during processing. This treatment involves continuously recirculating the slurry from a holding vessel that is being stirred through a media mill at a flow rate of 100 g / min by a peristaltic pump. The processing temperature was maintained at 20 ° C ± 5 ° C during milling. Residence time, 10 minutes, 20 minutes, 40 minutes, and 60 minutes
A 10 g sample was removed during milling in minutes and the particle size distribution was characterized as in Example 1.

After a residence time of 60 minutes, 50 μm polystyrene grinding media was added to the slurry with recirculation through the media mill. This 50 μm medium is 500
It was small enough to pass through a stirred bed of μm media and through a 100 μm media separator gap. In this way, the larger 50
Milling was achieved with both 0 μm media and smaller 50 μm media. Residence time at the crushing stage: 80 minutes, 10
Samples were removed at 0 and 120 minutes and 50μ media was removed using an 8μ filter. The properties of this sample were described as before. Sample retention time (min) Medium size (μm) Average diameter (nm) 3-1 10 500 277.1 3-2 20 500 208.1 3-3 40 500 206.3 3-4 60 500 191.3 3- 5 80 50 + 500 156.5 3-6 100 50 + 500 136.9 3-7 120 50 + 500 124.4 50 μm After adding media to this system, it is further ground to a very small average particle size. After treatment, there was no evidence of erosion or failure of the smaller media by the larger media.

Example 4 Another aqueous premixed slurry, the same as that used in Example 3, was prepared by simply mixing the following components: Component Amount (g) Dye D-2 50 Oleoylmethyltaurine, Sodium salt 10 Water 440 Total 500 This slurry was mixed with 625 g of polystyrene grinding media with an average diameter of 50 μm. A mixture of this filter dye slurry was added to 0.6 liter of Dyno Mil as in Example 1.
l, treated with a residence time of 120 minutes, to characterize as before, 20 minutes, 40 minutes, 60 minutes, and 12 minutes
The sample was removed at 0 minutes. Residence time (min) Mean diameter (nm) 20 245.4 40 196.1 60 174.4 120 127.3 These data allow the treatment described in Example 1 to be applied to materials of other compositions and their Confirm that it can be an effective means of particle size reduction of materials.

[0048]

Materials such as compounds useful in imaging elements are ground in a continuous process using fine particle grinding media to obtain submicron particles. It is another advantage of the present invention to provide a milling method that allows the use of very fine milling media (eg particles smaller than 300 μm) in a continuous milling process.

A further advantage of the present invention is to provide a continuous milling process which avoids the problems associated with prior art processes that require separation of the dispersed compound from the milling media in the milling chamber (eg separation screen clogging). It is to be.
Also, an advantage of the present invention is that it provides a method of micronizing compounds useful in imaging elements that generates little heat and reduces potential heat related problems such as chemical instability and contamination. is there.

[Brief description of drawings]

1 represents a graph of the particle size number (A) and weight (B) distribution of the unmilled premixed slurry of Example 1. FIG.

FIG. 2 depicts a graph of particle size number (A) and weight (B) distribution for the milled slurry of Example 1.

FIG. 3 represents a graph of the particle size number (A) and weight (B) distribution of the milled slurry of Example 2.

FIG. 4 is a schematic diagram of a preferred embodiment of the continuous grinding process of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 ... Compound useful for an image forming element 12 ... Hard grinding medium 14 ... Grinding chamber 16 ... Rotating shaft 18 ... Peristaltic pump 20 ... Holding tank

Claims (3)

[Claims] 1. A method for the continuous preparation of submicron particles of a compound useful in imaging, comprising the steps of: a) continuously introducing said compound and a hard grinding medium into a grinding chamber; b) said compound. To reduce the particle size of the compound in the grinding chamber, c) continuously removing the compound and the grinding medium from the grinding chamber, and then d) the grinding medium. Separating the compound from. 2. The method of claim 1, wherein the medium has an average particle size of 300 μm or less. 3. The method of claim 1, wherein the grinding media are polymeric resin beads.